between Pantellaria and Sciacca, 517 



two longitudinal hills, connected by intermediate low land 

 sending up smoke and vapour in abundance. The circular 

 basin, the centre of theis land, was full of boiling salt water 

 of a dingy red colour ; and the vapour was very oppressive, 

 causing nausea and faintness. 



Captain Senhouse informs us that the fragments of rock 

 brought away by the Hind cutter are compact and heavy, 

 and that the whole surface of the island is dense and perfectly 

 hard under the feet. No variety of lava was procured, nor 

 even any jet or streams of lava seen ; and Mr. Osborne, sur- 

 geon to His Majesty's ship Ganges, states that the substances 

 of which the island is composed are chiefly ashes, the pul- 

 verised remains of coal deprived of its bitumen, iron scoriae, 

 and a kind of ferruginous clay, or oxided earth. The scoriae 

 occur in irregular masses, some compact, dense, and sono- 

 rous, others light, friable, and amorphous, with metallic lustre, 

 slightly magnetic, barely moving the loadstone. A piece of 

 limestone was also found thrown up with the other sub- 

 -jstances, having no marks of combustion. There were, 

 according to the same observer, no traces of lava, no terra 

 puzzolana, no pumice, nor other stones, usually found on vol- 

 canic hills. 



The principal phenomena attendant on the elevation of 

 Graham Island are the form of the ejected mass and its 

 composition ; and more information will be contained in the 

 study of these two features, than in any hypothetical surmises 

 on the mode of ejection, and on the character and nature of 

 the action by which this took place. 



It will at once be observed, in the sketches of the island 

 which accompany this notice, that its appearance differs very 

 much according to the distance at which it is viewed. In 

 Jig, 11 1. it is the summit of a volcano, a cone of eruption slightly 

 elevated above the level of the sea; but, on a nearer approach, 

 its form is found to be that of a circular crater with more or 

 less perpendicular walls {Jig. 112.), like most of the craters of 

 elevation surrounding the internal craters of volcanoes, or the 

 islands and insulated formations of supposed similar origin. 

 The internal crater on the left-hand side of^/ig. 112., which 

 presents the most striking manifestation of this disposition, 

 has been obliterated in the sketch contained in the Journal of 

 the Royal Geographical Society, and occupied by smoke and a 

 prodigious flash of lightning. 



There is every reason to believe that volcanic eruptions 

 take place at the bottom of the sea, in the same manner as on 

 the surface of a continent; and Mr. Osborne points out the 



• N N 2 



